The field of the invention relates generally to ablative materials, and more specifically to a hybrid ablative thermal protection system.
Ablative materials have been used in a variety of applications to protect and insulate structures that are subjected to extreme thermal conditions. For example, many aerospace vehicles that traverse, exit, and enter the atmosphere of the Earth travel at high velocities, and as a result, their exterior aerosurfaces, and to some degree their substructure, experience high aerothermal loads. Aerothermal loads have been managed using a variety of techniques including insulation, radiant cooling, active cooling, conduction and convective cooling, and by phase change or ablative materials. Generally, ablative materials are applied to the affected aerosurfaces to absorb the extreme heat in order to insulate the vehicle from the thermal environment.
The thermal management technique of ablation has been widely used for a variety of applications since the early 1930s. Ablative materials were used in early rocket systems for nose cap protection and have also been used as re-entry heat shields on the Gemini and Apollo space vehicles, and further on many modern rocket nozzles. Many of these materials, although suitable for use in the aforementioned applications, have handling and longevity issues that preclude application on a system that is subjected to frequent handling and that may be stored for several years prior to use.
Known ablative materials comprise a variety of constituent components, each at certain percentages by weight or volume, to achieve the desired level of thermal protection and other physical properties. Generally, ablator compositions are a composite material comprising a resin matrix with a variety of filler materials to reduce the overall density or provide other physical properties.
Certain ablative compositions have included a variety of other constituent elements such as metal fillers, colloidal clay fillers, boron and oxygen compounds, polyurethane resins, a mixture of both epoxy and polysulfide resins, and many others too numerous to detail herein. The known art compositions, however, include numerous fillers to achieve a desired set of properties such as thermal, mechanical, and others. As a result, such compositions may be costly and difficult to fabricate with a relatively large number and variety of fillers. In addition, many known art ablator compositions demonstrate relatively low thermal and abrasion resistance performance under high heat flux and pressure loads, for example, as observed in Mach 6 to 8 vehicles.
Ablators with high shear, high heat flux capabilities generally have high densities. Lightweight thermal protection systems cannot withstand high shear, high heat flux environments. Accordingly, there remains a need in the art for an ablator composition that is reduced in weight from known ablative solutions that also improves thermal performance. Such an ablator would be low in density yet high in abrasion resistance and durability before, during, and after high thermal loads. The preferred ablator would also be relatively low cost and simple to fabricate.